Furnace system with internal flue gas recirculation

ABSTRACT

A furnace system  10  including a combustion vessel  12  having an outlet end  19  and at least one aperture  20, 22  extending into an interior area  14  defined by the combustion vessel. The furnace system  10  includes a flue duct  42  coupled to the outlet end  19  and in fluid communication with the interior area. A recirculation duct  55  extends from the flue duct  42  to one or more of the apertures  20, 22  and provides fluid communication between the flue duct  42  and the interior area  14.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application No.61/075,451 filed Jun. 25, 2008, the contents of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to a fossil fuel fired furnacesystem, and more particularly, to an oxyfuel fired furnace system havingan internal flue gas recirculation system.

BACKGROUND

Steam generators, also referred to as boilers or furnaces, are used invarious systems. For example, boilers can be used to produce steam foruse in electric turbines and in chemical processes for providing energyto initiate a chemical reaction. The combustion process employed inboilers often utilizes fossil fuels such as coal or oil. Generally,during the combustion process pollutants such as unburned fuel,particulate, ash, NOx and other combustion byproducts are generated. Ifallowed to enter the atmosphere in sufficient amounts, these pollutantscan detrimentally impact the environment and pose health hazards tohumans and animals.

SUMMARY OF THE INVENTION

According to aspects illustrated herein, there is provided a furnacesystem including a combustion vessel. A flue duct is coupled to anoutlet end of the combustion vessel and is in fluid communication withan interior area defined thereby. A recirculation duct also forms aportion of the furnace system and extends outwardly from the flue ductand provides fluid communication between the flue duct and the interiorarea of the combustion vessel.

According to other aspects disclosed herein, a conveying device isdisposed at least partially in the recirculation duct for facilitatingflow of one or more fluids through the recirculation duct into theinterior area of the combustion vessel in response to commands issuedfrom a controller. The conveying device can include an eductor forconveying a fluid such as, but not limited to oxygen, steam, flue gas orcombinations thereof into the interior area defined by the combustionvessel.

The above described and other features are illustrated by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the Figures, which are exemplary embodiments, andwherein like elements are numbered alike:

FIG. 1 schematically illustrates a furnace system in accordance with thedisclosure herein;

FIG. 2 schematically illustrates the furnace system of FIG. 1 with aneductor type conveying device;

FIG. 3 schematically illustrates a portion of the furnace system of FIG.1 and shows a fan-type conveying device; and

FIG. 4 is a cross sectional view of the furnace system of FIG. 1 showinga tangential firing configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a furnace system, generally designated by thereference number 10, includes a combustion vessel 12 defining aninterior area 14. The combustion vessel 12 also defines a hopper 18 at alower portion of an end 16 thereof. Generally opposite the hopper 18,the combustion vessel 12 defines a conduit 19 which during operation,conveys flue gases FG out of the combustion vessel. In the illustratedembodiment, the combustion vessel 12 also defines a first and a secondaperture, 20 and 22 respectively, that open into the interior area 14.

Still referring to FIG. 1, a manifold 24 or wind box is coupled to thecombustion vessel 12 and is in fluid communication with the interiorarea 14. The manifold 24 has an inwardly facing opening 26 and twooutwardly facing openings 28 and 30. In the illustrated embodiment, themanifold 24 wraps around a portion of the combustion vessel 12. Inaddition, a portion of the manifold 24 adjacent to the inwardly facingopening 26 sealingly engages a portion of an outside surface 32 of thecombustion vessel 12. Portions of the manifold 24 are positioned over atleast one of the first and second apertures, 20 and 22 respectively,such that an interior area 34 defined by the manifold is in fluidcommunication with the interior area 14 of the combustion vessel 12.

The interior area 14 of the combustion vessel 12 is also in fluidcommunication with flue duct 42 for facilitating the flow of flue gas FGtherethrough. Similarly, flue duct 44 is in fluid communication with theflue duct 42 as well as with a second hopper section 46. A first heatexchanger, for example an economizer 45, is positioned in and is influid communication with the flue duct 44. During operation, theeconomizer 45 cools the flue gas FG flowing therethrough. A second heatexchanger 50, such as an air preheater, is positioned downstream of andis in fluid communication with the flue duct 44 via, in the illustratedembodiment, conduit 48. A second conduit 52 extends between and is influid communication with the flue duct 44 and the manifold 24. Thesecond conduit 52 extends from the flue duct 44 downstream of an outlet47 of the economizer 45.

While the economizer 45 is described as being one potential means ofcooling the flue gas FG, other heat exchanger means may be employed,such as but not limited to ultra critical steam panels, steam heatingmeans, steam production means and combinations thereof without departingfrom the broader aspects disclosed herein.

The second conduit 52 and the manifold 24 cooperate to define arecirculation duct 55 which provides fluid communication between theflue duct 44 and the interior area 14 of the combustion vessel 12. Thesecond conduit 52 can be installed during initial construction of thefurnace system 10 or can be installed during a retrofit operation, afterinitial construction. The furnace system 10 also includes a pollutioncontrol system 54 in fluid communication with, and positioned downstreamof, the second heat exchanger 50.

The furnace system of FIG. 2 is similar to that illustrated in FIG. 1,therefore like elements are assigned like numerals, preceded by thenumber 1. Accordingly the furnace system, generally designated by thereference number 110, includes a combustion vessel 112 defining aninterior area 114. The combustion vessel 112 defines a first and asecond aperture 120 and 122, respectively, that open into the interiorarea 114. A manifold 124 or wind box is coupled to the combustion vessel112 and is in fluid communication with the interior area 114. Themanifold 124 is positioned over at least one of the first and secondapertures 120 and 122, respectively, such that an interior area 134defined by the manifold is in fluid communication with the interior area114 of the combustion vessel 112.

The interior area 114 of the combustion vessel 112 is in fluidcommunication with flue duct 142 for facilitating the flow of flue gasFG therethrough. Similarly, flue duct 144 is in fluid communication withthe flue duct 142. A first heat exchanger, for example an economizer 145is positioned in and is in fluid communication with the flue duct 144. Asecond conduit 152 extends between and is in fluid communication withflue duct 144 and the manifold 124. The second conduit 152 extends fromthe flue duct 144 downstream of an outlet 147 of the economizer 145. Asecond heat exchanger 150, such as an air preheater, is positioneddownstream of and is in fluid communication with the flue duct 144 via,in the illustrated embodiment, conduit 148. The second conduit 152 andthe manifold 124 cooperate to define a recirculation duct 155 whichprovides fluid communication between the flue duct 144 and the interiorarea 114 of the combustion vessel 112. The furnace system 110 furtherincludes a pollution control system 154 in fluid communication with, andpositioned downstream of, the second heat exchanger 150.

Still referring to FIG. 2, an eductor 156 is positioned in the secondconduit 152 for facilitating flow of one or more fluids into theinterior area 114 of the combustion vessel 112 in response to commands,for example a command signal regarding combustion vessel temperatureregulation, steam production and/or steam parameter measurement, issuedfrom a controller 178 such as, but not limited, to a computer orprogrammable logic controller. A motive fluid, such as oxygen, issupplied to a portion 158, such as a central portion, of the eductor 156at a predetermined pressure (e.g., 5 to 50 psig). An air streamdesignated by arrow A, flows into an air separation unit 160 whichseparates nitrogen from the air and supplies oxygen to the eductor 156via suitable piping 162. Flow of pressurized oxygen into the centralportion 158 of the eductor, possibly by a nozzle, causes flue gas FG tobe entrained into an inlet 164 of the eductor and discharged through anoutlet 166 of the eductor together with the oxygen into the interiorarea 134 of the manifold 124 and into the interior area 114 of thecombustion vessel 112.

While the air separation unit 160 is shown and described as supplyingoxygen to the eductor 156, it is contemplated that other means ofsupplying the oxygen can be employed, including but not limited to anoxygen sources such as oxygen tanks and/or cylinders in addition to orin place of the air separation unit.

Recirculation of a portion of the flue gas FG into the combustion vessel112 helps regulate furnace temperatures and steam conditions within apredetermined range and allows a greater mass flow of gas through thecombustion vessel. In addition, recirculation of the flue gas FG intothe combustion vessel reduces the overall mass flow rate of flue gasflowing downstream of the flue duct 144. The introduction of oxygen (orany low nitrogen fluid) into the combustion vessel 112 reducespollutants and the recirculation of flue gas FG into the combustionvessel 112 reduces the mass flow rate of the flue gas FG to be treatedby the pollution control system 154, thus smaller, less costly secondheat exchangers 150 and pollution control systems can be employed.

Although, oxygen is described as the motive fluid for use in the eductor156, other fluids can be employed including but not limited to steam,flue gas, flue gas processed by the pollution control system 154 or acombination thereof. While the eductor 156 is shown and described asbeing positioned in the second conduit 152 for discharging oxygen andflue gas FG into the combustion vessel 112, other devices for conveyingthe flue gas into the combustion vessel can be employed including butnot limited to a compressor, fan or blower as illustrated in FIG. 3 asdescribed below. Although the eductor 156 is shown and described asbeing positioned in the second conduit 152, it is contemplated thatportions of the eductor may extend outside of the second conduit, forexample into the manifold 124, into the flue duct 144 and/or protrudeinto an external area 159 outside of the second conduit.

The furnace system of FIG. 3 is similar to that illustrated in FIG. 1,therefore like elements are assigned like numerals, preceded by thenumber 2. As illustrated in FIG. 3, the furnace system 210 includes afan 270 disposed in the second conduit 252 for conveying flue gas FGfrom the flue duct 244 into the interior area 214 of the combustionvessel 212. The fan 270 is coupled to a drive unit (not shown) whichoperates the fan in response to a command signal, for example a commandsignal regarding combustion vessel temperature regulation, steamproduction and/or steam parameter measurement, issued by a controller278 such as, but not limited to, a computer or programmable logiccontroller.

While a fan 270 is shown and described for conveying the flue gas FGfrom the duct 244 into the combustion vessel 212, other devices such as,but not limited to, blowers and compressors can be employed withoutdeparting from the broader aspects disclosed herein. Although the fan270 is shown and described as being positioned in the second conduit252, it is contemplated that portions of the fan and/or drive unit mayextend outside of the second conduit, for example into the manifold 224,into the flue duct 144 and/or protrude into the external area 159outside of the second conduit.

The furnace system of FIG. 4 is similar to that illustrated in FIG. 1,therefore like elements are assigned like numerals, preceded by thenumber 3. Referring to FIG. 4, a tangentially fired furnace 310 includesa combustion vessel 312 having an interior area 314. The combustionvessel 312 is illustrated with four apertures 320, 321, 322 and 323extending therethrough. A lance 380, 381, 382 and 383 is positioned inrespective ones of the apertures 320, 321, 322 and 323 and oriented at apredetermined angle T measured from respective adjacent portions of thecombustion vessel 312. The angle T is of an appropriate magnitude, forexample an acute angle, to cause a fluid, such as oxygen, and fuelflowing through the lance to rotate in the interior area 314 as shown bythe arrows R. The lances 380, 381, 382 and 383 extend into the interiorarea 336 of the combustion chamber 312 for improved control of thecombustion process. While the lances 380, 381, 382 and 383 are shown anddescribed as being positioned in respective ones of the apertures 320,321, 322 and 323 and oriented at a predetermined angle T measured fromrespective adjacent portions of the combustion vessel 312, it iscontemplated that nozzles can be substituted for or positioned on adistal end of the lances.

Referring back to FIG. 2, during operation, fuel F, such as pulverizedcoal, is conveyed into the interior area 134 of the manifold 124 throughthe opening 128 and into the interior area 114 of the combustion vessel112 for initiation of combustion. The fuel F can be blown into themanifold 24 along with a combustion fluid such as oxygen. As a result ofthe combustion, flue gas FG exits the conduit end portion 119 of thecombustion vessel 112 and flows through the flue ducts 142 and 144,respectively, to the second heat exchanger 150 and to the pollutioncontrol unit 154 for processing. A portion of the flue gas FG isre-circulated to the combustion vessel 112 through the second conduit152 by operation of the eductor 156. The eductor 156 operates inresponse to a command signal, for example a command signal regardingcombustion vessel temperature regulation, steam production and/or steamparameter measurement, generated from the controller 178. Operation ofthe eductor 156 causes pressurized oxygen to flow through the eductorand thereby entrain flue gas from the flue duct 144. The eductor 156discharges the oxygen and the flue gas FG into the interior area 134 ofthe manifold 124 and into the interior area 114 of the combustion vessel112. The oxygen is provided to the eductor 156 by the air separationunit 160.

While the invention has been described with reference to variousexemplary embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A furnace system comprising: a combustion vessel having an outlet endand at least one aperture extending into an interior area defined bysaid combustion vessel; a flue duct coupled to said outlet end and influid communication with said interior area; and a recirculation ductextending from said flue duct to said at least one aperture andproviding fluid communication between said flue duct and said interiorarea.
 2. The furnace system of claim 1, further comprising conveyingmeans disposed at least partially in said recirculation duct for causingflow of at least one fluid through said recirculation duct into saidinterior area in response to a command issued from a controller.
 3. Thefurnace system of claim 2, wherein said conveying means comprises atleast one of a fan and a blower and a compressor.
 4. The furnace systemof claim 2, wherein said conveying means comprises an eductor having amotive fluid supplied thereto for conveying said at least one fluid andsaid motive fluid into said interior area.
 5. The furnace system ofclaim 4, wherein said motive fluid is oxygen.
 6. The furnace system ofclaim 4, wherein said motive fluid is steam.
 7. The furnace system ofclaim 4, wherein said motive fluid is flue gas.
 8. The furnace system ofclaim 1, further comprising: a pollution control system in communicationwith said flue duct for processing flue gas discharged from saidinterior area; an air preheater in fluid communication with said flueduct; and wherein said recirculation duct is positioned upstream of atleast one of said pollution control system and said air preheater. 9.The furnace system of claim 8, further comprising: conveying meansdisposed at least partially in said recirculation duct for causing flowof at least one fluid through said recirculation duct into said interiorarea in response to a command issued from a controller; wherein saidconveying means comprises an eductor having a motive fluid suppliedthereto for conveying said at least one fluid and said motive fluid intosaid interior area; and wherein said flue gas is supplied from saidpollution control system.
 10. The furnace system of claim 2, whereinsaid at least one fluid is flue gas.
 11. The furnace system of claim 1,wherein said furnace is tangentially-fired for combusting a fuel in thepresence of oxygen.
 12. A furnace system comprising: a combustion vesselhaving an outlet end and at least one aperture extending into aninterior area defined by said combustion vessel; a flue duct coupled tosaid outlet end and in fluid communication with said interior area; arecirculation duct extending from said flue duct to said at least oneaperture and providing fluid communication between said flue duct andsaid interior area; and an eductor disposed at least partially in saidrecirculation duct and having oxygen supplied thereto for conveying atleast some of said flue gas and said oxygen through said recirculationduct into said interior area.
 13. The furnace system of claim 12,wherein at least one lance extends through said at least one apertureand into said interior area, said lance having a passage extendingtherethrough for conveying a portion of said oxygen through said lanceinto said interior area.
 14. The furnace system of claim 12, wherein atleast one nozzle extends through said at least one aperture and intosaid interior area, said nozzle having a passage extending therethroughfor conveying a portion of said oxygen through said nozzle into saidinterior area.
 15. The furnace system of claim 12, further comprising: apollution control system in communication with said flue duct forprocessing flue gas discharged from said interior area; an air preheaterin fluid communication with said flue duct; and wherein saidrecirculation duct is positioned upstream of at least one of saidpollution control system and said air preheater.